Field of the Disclosure
The present invention relates to a display device and an array substrate for a display device and, more particularly, to a display device and an array substrate for a display device in which a contact defect between a bump and a driving chip is prevented.
Related Art
In general, a liquid crystal display (LCD) device is driven using optical anisotropy and polarization qualities of liquid crystal. The liquid crystal is thin and long in structure, having orientation in molecular alignment, and the orientation of molecular alignment of liquid crystals may be controlled by intentionally applying an electric field to the liquid crystal. Thus, if the orientation of molecular alignment of liquid crystal is arbitrarily adjusted, the molecular alignment of liquid crystal becomes varied such that light is refracted in a direction toward the molecular alignment of liquid crystal due to optical anisotropy, thereby expressing image information.
The LCD device, having an active matrix structure in which thin film transistors (TFTs) and pixel electrodes connected to the TFTs are arranged in a matrix form to obtain excellent resolution and video implementation capability, has come to prominence. The above-mentioned LCD device includes a color filter substrate on which a common electrode is formed, an array substrate on which a pixel electrode is formed, and liquid crystal interposed between the two substrates. In the LCD device, an electric field applied between the common electrode and the pixel electrode drives liquid crystal, exhibiting excellent characteristics in terms of transmission ratio and an aperture ratio.
FIG. 1 is a plan view illustrating a related art array substrate for a display device, FIG. 2 is a cross-sectional view illustrating a bump, FIG. 3 is a plan view illustrating the bump, FIG. 4 is a scanning electron microscope (SEM) image of the bump, FIG. 5 is an image of a driving chip bonded to the bump, FIG. 6 is an image of an indentation of the bump and the driving chip, and FIG. 7 is an image illustrating a defective display device.
Now Referring to FIG. 1, a related art array substrate 10 for a display device includes a display area 11 which is an active area (A/A) for displaying an image and a non-display area 12. A chip on glass (COG) unit 13, to which a driving chip (D-IC) for applying a driving signal is bonded, is positioned in the non-display area 12, and a flexible printed circuit (FPC) pad unit 14, to which an FPC for applying an external driving signal to the driving chip is attached, is positioned in the non-display area 12. A plurality of bumps 20 connected to the driving chip are provided in the COG unit 13.
Referring to FIG. 2, the bumps 20 positioned in the COG unit 13 include a pad 22 positioned on a substrate 21 and a bump electrode 27 connected to the pad 22. In detail, the pad 22 is positioned on the substrate 21, and an insulating layer 23 including an open portion 24 exposing the pad 22 is positioned. A first metal layer 25 and a second metal layer 26 are positioned on the pad 22 exposed by the open portion 24 of the insulating layer 23. The first metal layer 25 is made of a titanium alloy, and the second metal layer 26 is made of gold (Au) to improve adhesion with the pad 22. The bump electrode 27 is disposed on the second metal layer 26 to be electrically connected to the pad 22.
Referring to FIGS. 3 and 4 together, the bump 20 configured as described above has a dimple 28 in the bump electrode 27 due to a difference between a thickness of the insulating layer 23 and a height of the open portion 24. The dimple 28 of the bump electrode 27 is formed to correspond to the difference between the thickness of the insulating layer 23 and the height of the open portion 24, and a planar area of the dimple 28 is formed to correspond to an area of the open portion 24.
Referring to FIGS. 5 and 6, when a driving chip is bonded to the COG unit including the bump with the dimple formed thereon through an anisotropic conductive film (ACF), conductive balls of the ACF cannot be firmly attached to the bump with the dimple formed thereon. As a result, as illustrated in FIG. 6, an indentation defect of the bump is observed in a rear surface of the substrate, and thus, the bump and the driving chip are determined as having defective contact. When the bump and the driving are defective in contact, a display defect appears as illustrated in FIG. 7. The display defect of a display device degrades productivity.